In the present study, human performance and alertness effects of 4 different nightly sleep durations (3, 5, 7, or 9 hours of sleep over 7 consecutive days) are compared and contrasted. Results will provide information regarding the rate at which recuperation occurs during sleep, and the differential effects that these various sleep durations have on that rate of recuperation. A minimum of 64 healthy subjects (both male and female drivers with a current CDL) spend 15 consecutive days in the residential clinical research facility at the General Clinical Research Center at Johns Hopkins Bayview Medical Center. For the first 3 days, subjects are trained on the various performance measures and allowed to habituate to the research environment (with 8 hrs of sleep per night). Results from the 4th day of testing constitute baseline performance. Subjects are then allowed either 3, 5, 7, or 9 hours of sleep (n = 16 per sleep duration group) over the next 7 nights (i.e., Day 4 through Day 10). Recovery sleep (8 hours per night) is allowed on the last 4 nights. Daytime measures (administered on a rigouous and consistent schedule across all days - training, baseline, experimental, and recovery) include simulated driving performance, various cognitive/psychomotor/mood tests from the Walter Reed Performance Assessment Battery, sleep latency tests, vital signs, continuous recordings of polysomnographic variables (EEG, EKG, EMG, EOG), eye tracking, actigraphy, the Synthetic Work Task, and a Group Decision Task. Results will be used to refine the Walter Reed Sleep/Performance Model - a model that will allow enhanced management of sleep and alertness during both military and civilian operations.